1. Field of the Invention
The present invention relates to an arrangement for coupling two co-axial shaft members, and more particularly, to provide an improved tapered coupling for transferring torsional forces and to provide improved stiffening of the shaft in the area of the coupling.
2. Description of the Prior Art
Gas turbine engines, especially small turbine engines, are often used for providing mechanical energy through a transmission or gearbox. The shaft of such an engine is designed to rotate at very high r.p.m.'s which may be in the order of 40,000 r.p.m. or higher.
It is necessary to couple the turbine engine shaft to a gearbox input pinion, and in view of the magnitude of the velocity, threaded or splined coupling arrangements tend to allow too great tolerances due possibly to a phenomenon referred to as "hoop stress" which is generated by the high centrifugal force. The result is reduced stiffness of the joint or coupling, and in the case of a threaded joint, a less efficient transfer of torsional forces.
Various attempts have been made in order to overcome the problems mentioned above as being inherent in shaft couplings in small turbine engines. West German Offenlegungsschrift 24 45 041, published Apr. 17, 1975 to Rolls Royce, suggests a shaft coupling including an axial splined section and tapered or conical rings engaging tapered sections of one of the shafts on either side of the splined section. The conical rings are secured by threaded sleeves. U.S. Pat. No. 3,718,957, issued Mar. 6, 1973 to W. C. Shank, shows an impeller hub secured by a tapered ring and a threaded nut. West German Auslegeschrift 27 47 319, published Apr. 5, 1979, shows another example of a shaft coupling using a conical ring with a threaded nut for coupling a shaft in small turbine engines. All of the above patents are concerned with preventing the axial displacement of the shafts being coupled.